It is common practice to include invisible security features into security ink. These features are used to enable end usersxe2x80x94such as banks and central cash sorting companiesxe2x80x94to identify false bank notes from true ones by inspecting these invisible features.
Up to now the usual practice has been to check the invisible properties of security ink used as security features at the end of the printing process. It results that the absence or defectiveness of such security features (which can happen for example if inks of a similar or identical colour but without the invisible properties are inadvertently mixed) is detected only once all the printing steps have been performed. In the case of bank notes printing, for example, the deficiency of the invisible security features may result in a large amount of waste notes or render the utility of the security feature null and void.
The present invention aims to remedy this drawback by constantly monitoring, in the ink fountain, the ink which is supposed to contain the invisible feature, whereby allowing to detect an eventual absence or a dilution of the invisible feature at the moment of printing. This enables rapid detection of the error and separation of the sheets with incorrect inking from those with good ink. The aim of the security feature is fully preserved and waste of printed sheets is avoided.
To this end, the present invention is concerned with a method for continuously checking the production of security printing machines comprising at least one ink fountain containing a security ink provided with an invisible feature, wherein an ink property detector with sensitivity in the range of said security feature is provided into a movable element being displaced into said ink fountain and in that the output of said detector is continuously collected and transmitted to a warning device.
The invention is also concerned with an application of said method for checking the production of printing machines comprising an ink fountain containing a security ink having a predetermined magnetic property, wherein an ink property detector provided with a ferromagnetic transducer sensitive to said magnetic property is used.
The invention is also concerned with a device for performing said method or said application, wherein the ink property detector is integrated to an ink-agitator comprising a finger element the tip of which extends into the ink fountain, said finger element being continuously displaced in said fountain and the ink property detector having an outlet connected to the warning device.
The integration of the ink property detector to an ink-agitator is particularly advantageous because it allows a detection in the fountain itself at the moment of printing, and also, since the detector is continuously moving into the ink fountain, because it allows the detection of the introduction of an inadequate ink at the very moment the ink is poured into the ink fountain.